Amplified extrachromosomal elements containing c-Myc and Pvt 1 in a mouse plasmacytoma.

After adaptation of a mouse plasma cell tumor, MOPC265, to culture, we have found several unique chromosomal alterations in addition to the T(12;15) translocation and trisomy 11 frequently observed in plasmacytomas. Among these alterations is a specific coamplification of the c-Myc and Pvt 1 gene loci from mouse chromosome 15. Further analysis by fluorescence in situ hybridization demonstrates that the amplicons of c-Myc and Pvt 1 exist as extrachromosomal elements as well as within intact chromosomes. Most importantly, the presence of both Pvt 1 and c-Myc in these extrachromosomal elements indicates ongoing coselection for these loci in the propagation of MOPC265.